Studies on two regulatory processes controlled by T4 will continue; process S1 (first shutoff) causes the shutoff of synthesis of T4 early proteins at around 12 min. at 37 degrees, while process S2 does the same at 20 min under conditions where S1 fails. We have shown that the T4 regA gene controls S2 for many early proteins. We have begun to examine ribosomes labeled with radioactive amino acids at various times before or after infection, to ask whether differences between wild-type T4 and a regA mutant can be detected by one- and two-dimensional electrophoresis. We are also attempting to isolate T4 mutants specifically defective in S1, in order to study the mechanism of S1, especially to learn whether it also affects translation, as S2 apparently does. Experiments indicate that the regA gene is involved in blocking the expression of early genes from recombinant parental DNA, and this is being studied further. We have found that the temperature sensitivity of a regA mutant is explained by underproduction of several T4 late proteins, including the products of genes 23 and 22; we are seeking a unifying model to explain these effects of the regA mutation and the effects on early protein synthesis. BIBLIOGRAPHIC REFERENCES: Wiberg, J.S. and Swanson, R.S., "das mutation in bacteriophage T4D does not suppress an amber mutation in T4 gene 59", J. Virol. 16, 1348-1350 (1975).